Which of these numbers is prime? ${3,\ 45,\ 64,\ 75,\ 95}$
Explanation: A prime number has exactly two factors: 1 and itself. The factors of 3 are 1 and 3. The factors of 45 are 1, 3, 5, 9, 15, and 45. The factors of 64 are 1, 2, 4, 8, 16, 32, and 64. The factors of 75 are 1, 3, 5, 15, 25, and 75. The factors of 95 are 1, 5, 19, and 95. Thus, 3 is a prime number.